It is accepted that a person with knowledge that a crime, or some other form of abuse, has been committed should convey that information to appropriate authorities in order that remedial measures may be taken and justice done. Where the authorities are themselves perceived as unjust or the abuse is defined by laws or regulations which are perceived as unjust, the informer is viewed as acting against the interests of the social group within which the so-called abuse took place. Informers are especially suspect when they act not for the promotion of the welfare of the society, however it is defined, but for payment or in a spirit of personal revenge. The negative consequences of their activities are increased when the information conveyed is false or deliberately misleading and when authorities actively encourage people to inform against each other.
Informers have existed in most cultures. The difficulties they create were recognized in the Code of Manu and especially from the early Roman Empire. Extensive use of networks of informers has traditionally been made by despots, dictators and repressive regimes. Their use has been encouraged in occupied countries and territories as a means of controlling the population and establishing a reign of fear. Such informers are subsequently judged as traitors to their country. Networks of informers have acquired a more organized form on the initiative of modern intelligence services.
Withholding information which could remedy an abuse or bring a criminal to justice makes a person party to that abuse. In many cases informers advance the cause of law and order when otherwise crime would flourish. Often the use of informers is the only means to break criminal networks and to prevent subversive or terrorist activities.